Since other than sensationalism the media mostly refused to do their job about these allegations it will be difficult to find any site that deals with these allegations in an extensive but balanced manner and is not considered a fan site or a hater site (the latter of course have their agenda and are not trustworthy).
But I think it is pretty fallacious thinking by your friend that information cannot be true or valuable if it's coming from fans. What makes newspapers, which have proven to be liars or totally ignorant about these cases over and over again, more trustable? What makes tabloids that even paid money to people to make up lies about these allegations, more independent? Treat fan sites with healthy scepticism and with critical eyes, but at least listen to them. A closed mind is not a good start to get informed about anything.
The Michael Jackson Allegations website gives sources that anyone can check out for themselves. Everything that is written there is sourced. It extenstively uses such sources as the accusers themselves - for example the Chandler's book or the Arvizo's testimonies. I think actually those are the sources it uses the most, so it's giving you an extensive look into what the allegations actually were, what their claims are, it presents the accuser's side extensively - what else can be done?
I think if your friend refuses to read fan written sites but you are eager to convince him maybe you should invest a bit of work in it and study the information on those sites yourself and present it to him in your own words. Referencing the sources like the Chandler book, Arvizo's testimonies etc.
As for books, there is Aphrodite Jones and she is not a fan. There is Geraldine Hughes and she is not a fan (she was the secretary of Barry Rothman).
You will never find a totally independent source on these allegations, since both sides, including the media, have their agendas or own POV. Actually, in life, you will rarelly find a totally independent source about ANYTHING, so if that's what your friend wants he may never find that about MOST subjects in life. When you watch the news, often the presentation or interpretation of it depends on which channel you watch it or in which paper you read it. Even when you read a school textbook it represents one POV that not everyone may agree with - especially about subjects such as history or social sciences. (Obviously there is less room for different POVs in subjects such as math.)
As a thinking person your job is to look at all that info and process it for yourself. Not necessarily accepting everything that is being told to you as the truth and also considering a source's bias. But an intelligent person can distinguish between facts and opinions whatever the source is.